Mapping the susceptibility of rain-triggered lahars at Vulcano island (Italy) combining field characterization, geotechnical analysis, and numerical modelling

Baumann, Valérie; Bonadonna, Costanza; Cuomo, Sabatino; Moscariello, Mariagiovanna; Biass, Sébastien; Pistolesi, Marco; Gattuso, Alessandro

doi:10.5194/nhess-19-2421-2019

Cited by 15 publications

(27 citation statements)

References 88 publications

(149 reference statements)

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“…Lahars bed thickness vary between 0.1 and 0.6 m in the middle and lower catchments of the cone (Baumann et al 2019). These loose and incoherent deposits cover the Tufi Varicolori layer, an impermeable substratum that favours the remobilisation of the overlying deposits through lahars generation (Ferrucci et al 2005).…”

Section: Geographical and Geological Setting Of The Study Areamentioning

confidence: 99%

“…Vulcanian cycle and subplinian eruptions of VEI (Volcanic Explosivity Index) 2 and 3. Baumann et al (2019) have used the associated probabilistic isomass maps to assess the scenario that would produce the most unstable deposit combining field characterization, geotechnical analysis, and numerical modelling with TRIGRS (Baum et al 2002). For the Vulcanian scenario, the largest unstable volume was reached for an eruption duration of 18 months, while the subplinian deposits, which are characterised by a smaller cohesion, become more stable with thickness increase depending on rainfall intensity and slope angle (Baumann et al 2019).…”

Section: Lahar Source Volume Estimationmentioning

confidence: 99%

“…Baumann et al (2019) have used the associated probabilistic isomass maps to assess the scenario that would produce the most unstable deposit combining field characterization, geotechnical analysis, and numerical modelling with TRIGRS (Baum et al 2002). For the Vulcanian scenario, the largest unstable volume was reached for an eruption duration of 18 months, while the subplinian deposits, which are characterised by a smaller cohesion, become more stable with thickness increase depending on rainfall intensity and slope angle (Baumann et al 2019). Given that a Vulcanian cycle has the highest probability of occurrence at this volcanic system (Selva et al 2020), in this study we consider the worst-case scenario identified by Baumann et al (2019) for the Vulcanian cycle (i.e.…”

Section: Lahar Source Volume Estimationmentioning

confidence: 99%

“…18 months of eruption duration with the characteristics of the last cycle occurred on Vulcano in 1888-90). Using a probabilistic isomass map compiled for a 25% probability of occurrence, Baumann et al (2019) used the model TRIGRS to estimate the potential triggering source at 22 upper catchments located in the northern sector of La Fossa cone (Fig. 3).…”

Section: Lahar Source Volume Estimationmentioning

confidence: 99%

“…Because the island is periodically affected by intense rainy events, lahar remobilization of tephra deposits is still nowadays an active process (e.g. Di Traglia et al 2013, Baumann et al 2019. Galderisi et al (2013) had already shown how the north of Vulcano island is the most exposed to lahars generation and, based on the characteristics of buildings and urban fabrics, is characterised by various degrees of vulnerability.…”

Section: Introductionmentioning

confidence: 99%

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Lahar Risk Assessment: the Case Study of Vulcano Island, Italy

Gattuso¹,

Bonadonna²,

Frischknecht³

et al. 2020

Preprint

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Lahars are rapid flows composed of water and volcaniclastic sediments, which have the potential to impact residential buildings and critical infrastructure as well as to disrupt critical services, especially in absence of a hazard-based land-use planning. Their destructive power is mostly associated with their velocity (related to flow rheology and surrounding topography) and to their ability to bury buildings and structures (related to the deposit thickness). The distance reached by lahars depends on their volume, on sediments/water ratio, as well as on the overall characteristics of the path where they propagate. Here we present a novel strategy for the assessment of risk associated with lahar inundation related both to flow velocity and deposit thickness using Vulcano island (Italy) as a case study. First, a range of hazard scenarios has been identified that are related to the mobilization by intense rain events of tephra fallout deposited on the slopes of the La Fossa cone by a future Vulcanian eruption. Second, a numerical model has been used to identify the potential lahar impact areas on the northern sector of Vulcano, where both residential and touristic facilities are present. In this specific case we have used the Smoothed Particle Hydrodynamic (SPH) model that provides information on both flow velocity and deposit thickness. Finally, exposure and vulnerability surveys were carried out in order to compile risk maps for both lahar-flow velocity and final lahar-deposit thickness. Our analyses show the importance of carrying out accurate and detailed risk assessments exploring a variety of initial conditions in order to best quantify the potential damage and identify suitable mitigation strategies.

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Section: Geographical and Geological Setting Of The Study Areamentioning

confidence: 99%

Section: Lahar Source Volume Estimationmentioning

confidence: 99%

Section: Lahar Source Volume Estimationmentioning

confidence: 99%

Section: Lahar Source Volume Estimationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Lahar Risk Assessment: the Case Study of Vulcano Island, Italy

Gattuso¹,

Bonadonna²,

Frischknecht³

et al. 2020

Preprint

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How rainfall influences tephra fall loading — an experimental approach

et al. 2021

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The load a tephra fall deposit applies to an underlying surface is a key factor controlling its potential to damage a wide range of assets including buildings, trees, crops and powerlines. Though it has long been recognised that loading can increase when deposits absorb rainfall, few efforts have been made to quantify likely load increases. This study builds on previous theoretical work, using an experimental approach to quantify change in load as a function of grainsize distribution, rainfall intensity and duration. A total of 20 laboratory experiments were carried out for ~ 10-cm thick, dry tephra deposits of varying grainsize and grading, taken to represent different eruptive scenarios (e.g. stable, waxing or waning plume). Tephra was deposited onto a 15° impermeable slope (representing a low pitch roof) and exposed to simulated heavy rainfalls of 35 and 70 mm h−1 for durations of up to 2 h. Across all experiments, the maximum load increases ranged from 18 to 30%. Larger increases occurred in fine-grained to medium-grained deposits or in inversely graded deposits, as these retained water more efficiently. The lowest increases occurred in normally graded deposits as rain was unable to infiltrate to the deposit’s base. In deposits composed entirely of coarse tephra, high drainage rates meant the amount of water absorbed was controlled by the deposit’s capillary porosity, rather than its total porosity, resulting in load increases that were smaller than expected. These results suggest that, for low pitch roofs, the maximum deposit load increase due to rainfall is around 30%, significantly lower than the oft-referenced 100%. To complement our experimental results, field measurements of tephra thickness should be supplemented with tephra loading measurements, wherever possible, especially when measurements are made at or near the site of observed damage.

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